In order to detect microbial pathogens in specimens, whether of human, animal or environmental origin, the following general procedure is commonly used: the target (and other) microbes in the specimen are, in the prior art, inoculated with the specimen into a culture medium in which they are provided with all the nutrients they require for growth. The specimen may be an untreated natural sample, or it may be a sample which has been pretreated as, for example, by membrane filtration. The culture medium has the nutrients and other selective chemicals such as antimetabolites or antibiotics, which are selectively active against microbes other than the target microbes. The culture medium is a "general medium", even with the selective chemicals, in that it supports the growth of both target microbes and related microbes and thus is only partially specific to the target microbes.
The culture medium, which may be a water solution or a water gel, is sterilized to rid it of any contaminating microbes which may be present in the medium and which could, therefore, interfere with the analysis. The culture medium must be refrigerated and packaged in such a way to avoid contamination after manufacture.
After one or more of the culture media are inoculated with the specimen, the inoculated media are incubated under controlled atmospheric conditions. After incubation, the culture media are examined for growth of any microbes. If such growth is observed, a sample thereof is taken for further analysis, since the presence of the target microbe can only be established by isolating it in the pure state, not mixed with other microbes. Once isolated on subsequent culture media, the target microbes are identified by testing for a variety of physical and chemical characteristics. If the apparent target microbe growths are not isolated, false negative tests can result.
It will be readily appreciated that this most common analytical procedure is time consuming and must be carefully performed to preserve sterility.